Radar sensors for motor vehicles are used to acquire the surrounding traffic conditions in the context of driver assistance systems, for example for radar-supported distance regulation (ACC; Adaptive Cruise Control). A driver assistance system of this type is discussed for example in the publication “Adaptive Fahrgeschwindigkeitsregelung ACC (Adaptive Speed Regulation ACC),” Robert Bosch GmbH, Gelbe Reihe series, 2002 ed., Technische Unterrichtung. In addition to distance and relative speed, an important measurement quantity of the radar sensor is also the angle of the located objects.
Here, both the horizontal angle (azimuth angle) and the vertical angle (elevation angle) are important. The azimuth angle is used to estimate the transverse offset, and is thus used for lane assignment. The elevation angle makes it possible to distinguish between objects that can be driven under or driven over and objects that are genuine obstacles. Thus, in particular in safety applications (PSS; Predictive Safety Systems), false alarms due to metallic objects such as manhole covers, metal cans on the road surface, and the like can be avoided.
The azimuthal angular resolution capacity is in most cases achieved in that a plurality of radar lobes are produced having an angular offset from one another, in which the radar echoes are evaluated in separate channels. Scanning radar systems are also known in which the radar lobe is pivoted in the horizontal direction. An estimation of the elevation angle is possible for example through mechanical pivoting of the radar sensor in the vertical direction. For reasons of cost, however, the elevation angle is usually determined only indirectly, via a temporal evaluation of the back-scatter characteristic of objects.
For use in radar sensors for motor vehicles, so-called planar antenna devices or patch antennas are particularly suitable, because, due to their flat configuration, they can be produced easily and at low cost, for example using an etching method. Such an antenna device is typically a planar configuration of radiating resonators on an RF substrate, each resonator being assigned a particular amplitude and phase. The directional characteristic of the antenna system then results through superposition of the radiation diagrams of the individual patch elements.
German patent document DE 102 56 524 A1 discusses a device for measuring angular positions using radar pulses and overlapping radiation characteristics of at least two antenna elements.